I'm going shell collecting - how do I know if it's really not living?

Some things are obvious, like the shell is empty. Or I could place it in a bucket of ocean water for a while and see if anything comes out or moves… but what about a sea star? Or a sea anemone? What if a sand dollar still has its fuzz, but none of the tube feet are moving? If a sea horse is not dried up, but in the wrack, can I put it back in the water and try to revive it first?